Laser-transparent polyesters with inorganic salts

ABSTRACT

Use of thermoplastic molding compositions comprising, as essential components,
         A) from 29 to 99.95% by weight of a polyester,   B) from 0.25 to 3.0% by weight of alkali metal oxoaluminates, or alkali metal salts of cyanic acid, isocyanic acid, thiocyanic acid, or metaboric acid, or a mixture of these,   based on 100% by weight of A) and B), and also moreover   C) from 0 to 70% by weight of further additives, where the total of the % by weight values for A) to C) is 100%,
 
for producing laser-transparent moldings of any type.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit (under 35 USC 119(e)) of U.S.Provisional Application 61/450,145, filed Mar. 8, 2011, which isincorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to the use of thermoplastic molding compositionscomprising as essential components

-   -   A) from 29 to 99.95% by weight of a polyester,    -   B) from 0.25 to 3.0% by weight of alkali metal oxoaluminates, or        alkali metal salts of cyanic acid, isocyanic acid, thiocyanic        acid, or metaboric acid, or a mixture of these,

based on 100% by weight of A) and B), and also moreover

-   -   C) from 0 to 70% by weight of further additives, where the total        of the % by weight values for A) to C) is 100%,        for producing laser-transparent moldings of any type.

The invention further relates to the use of the laser-transparentmoldings for producing moldings by means of laser transmission weldingprocesses, the processes for producing moldings of this type, and alsoto the use of these in various application sectors.

Components B) of this type are nucleating agents for PET and relatedpolyesters. By way of example, the use of sodium thiocyanate in PET isdescribed in U.S. Pat. No. 4,405,741 and the use of sodium nitrite inPET is described in U.S. Pat. No. 4,349,505. The optical properties ofthe compounded materials were not investigated.

There are various processes (Kunststoffe 87, (1997), 11, 1632-1640) forwelding plastics moldings. In the case of the widely used processes ofheated-tool welding and vibration welding (e.g. of motor-vehicle inletmanifolds), precondition for a stable weld is adequate softening of theadherends in the contact zone prior to the actual step that produces thejoin.

Laser transmission welding is a method providing an alternative tovibration welding and heated-tool welding, and has seen a constantincrease in its use in recent times, in particular with use of diodelasers.

The technical literature describes the fundamental principles of lasertransmission welding (Kunststoffe 87, (1997) 3, 348-350; Kunststoffe 88,(1998), 2, 210-212; Kunststoffe 87 (1997) 11, 1632-1640;Plastverarbeiter 50 (1999) 4, 18-19; Plastverarbeiter 46 (1995) 9,42-46).

Precondition for the use of laser transmission welding is that theradiation emitted from the laser first passes through a molding whichhas adequate transparency for laser light of the wavelength used, andwhich in this patent application is hereinafter termed laser-transparentmolding, and is then absorbed, in a thin layer, by a second moldingwhich is in contact with the laser-transparent molding and whichhereinafter is termed laser-absorbent molding. Within the thin layerthat absorbs the laser light, the energy of the laser is converted intoheat, which leads to melting within the contact zone and finally tobonding of the laser-transparent and of the laser-absorbent molding viaa weld.

Laser transmission welding usually uses lasers in the wavelength rangefrom 600 to 1200 nm. In the wavelength range of the lasers used forthermoplastics welding, it is usual to use Nd:YAG lasers (1064 nm) orhigh-power diode lasers (from 800 to 1000 nm). When the termslaser-transparent and laser-absorbent are used hereinafter, they alwaysrefer to the abovementioned wavelength range.

A requirement for the laser-transparent molding, in contrast to thelaser-absorbent molding, is high laser transparency in the preferredwavelength range, so that the laser beam can penetrate as far as theweld area, with the necessary energy. By way of example, transmittancefor IR laser light is measured by using a spectrophotometer and anintegrating photometer sphere. This measurement system also detects thediffuse fraction of the transmitted radiation. The measurement iscarried out not merely at one wavelength but within a spectral rangewhich comprises all of the laser wavelengths currently used for thewelding procedure.

Users presently have access to a number of laser-welding-processvariants based on the transmission principle. By way of example, contourwelding is a sequential welding process in which either the laser beamis conducted along a freely programmable weld contour or the componentis moved relatively to the immovable laser. In the simultaneous weldingprocess, the linear radiation emitted from individual high-power diodesis arranged along the weld contour to be welded. The melting and weldingof the entire contour therefore takes place simultaneously. Thequasi-simultaneous welding process is a combination of contour weldingand simultaneous welding. Galvanometric mirrors (scanners) are used toconduct the laser beam at a very high velocity of 10 m/s or more alongthe contour of the weld. The high traverse rate provides progressiveheating and melting of the region of the join. In comparison with thesimultaneous welding process, there is high flexibility for alterationsin the contour of the weld. Mask welding is a process in which a linearlaser beam is moved transversely across the adherends. A mask is usedfor controlled screening of the radiation, and this impacts the area tobe joined only where welding is intended. The process can produce veryprecisely positioned welds. These processes are known to the personskilled in the art and are described by way of example in “HandbuchKunststoff-Verbindungstechnik” [Handbook of plastics bondingtechnology](G. W. Ehrenstein, Hanser, ISBN 3-446-22668-0) and/orDVS-Richtlinie 2243 “Laserstrahlschweiβen thermoplastischer Kunststoffe”[German Welding Society Guideline 2243 “Laser welding ofthermoplastics”].

Irrespective of the process variant used, the laser welding process ishighly dependent on the properties of the materials of the twoadherends. The degree of laser transparency (LT) of the transparentcomponent has a direct effect on the speed of the process, through theamount of energy that can be introduced per unit of time. The inherentmicrostructure, mostly in the form of spherulites, of semicrystallinethermoplastics generally gives them relatively low laser transparency.These spherulites scatter the incident laser light to a greater extentthan the internal structure of a purely amorphous thermoplastic:back-scattering leads to a reduced total amount of transmitted energy,and diffuse (lateral) scattering often leads to broadening of the laserbeam and therefore to impaired weld precision. These phenomena areparticularly evident in polybutylene terephthalate (PBT), which incomparison with other thermoplastics that crystallize well, such as PA,exhibits particularly low laser transparency and a high level of beamexpansion. PBT therefore continues to be comparatively little used asmaterial for laser-welded components, although other aspects of itsproperty profile (e.g. good dimensional stability and low waterabsorption) make it very attractive for applications of this type.Although semicrystalline morphology is generally unhelpful for highlaser transparency, it provides advantages in terms of other properties.By way of example, semicrystalline materials continue to have mechanicalstrength above the glass transition point and generally have betterchemicals resistance than amorphous materials. Materials thatcrystallize rapidly also provide processing advantages, in particularquick demoldability and therefore short cycle times. It is thereforedesirable to combine semicrystallinity with rapid crystallization andhigh laser transparency.

There are various known approaches to laser-transparency improvement inpolyesters, in particular PBT. In principle, these can be divided intoblends/mixtures and refractive-index matching.

The approach using blends/mixtures is based on “dilution” of thelow-laser-transparency PBT by using a high-laser-transparency partner inthe blend/mixture. Examples of this are found in the followingspecifications: JP2004/315805A1 (PBT+PC/PET/SA+filler+elastomer),DE-A1-10330722 (generalized blend of a semicrystalline thermoplasticwith an amorphous thermoplastic in order to increase LT; spec.PBT+PET/PC+glass fiber), JP2008/106217A (PBT+copolymer with1,4-cyclohexanedimethanol; LT of 16% increased to 28%). A disadvantagehere is that the resultant polymer blends inevitably have propertiesmarkedly different from those of products based predominantly on PBT asmatrix.

The refractive-index matching approach is based on the differentrefractive indices of amorphous and crystalline PBT, and also of thefillers. By way of example, comonomers have been used here:JP2008/163167 (copolymer of PBT and siloxane), JP2007/186584(PBT+bisphenol A diglycidyl ether) and JP2005/133087(PBT+PC+elastomer+high-refractive-index silicone oil) may be mentionedas examples. Although this leads to an increase in laser transparency,this is achieved with loss of mechanical properties. Therefractive-index difference between filler and matrix can also bereduced, see JP2009/019134 (epoxy resin coated onto glass fibers inorder to provide matching at the optical interface between fiber andmatrix), or JP2007/169358 (PBT with high-refractive-index glass fiber).Starting materials of this type are, however, disadvantageous because oftheir high costs and/or the additional stages that they require withinthe production process.

The effects achieved in relation to laser-transparency increase are alsooverall relatively minor and therefore not entirely satisfactory.

A SUMMARY OF THE INVENTION

The object of the present invention was therefore to improve the lasertransparency of polyesters. The molding compositions defined in theintroduction were accordingly found. The dependent claims give preferredembodiments.

The invention relates to a process for producing a laser-transparentmolding which comprises utilizing a thermoplastic molding compositioncomprising, as essential components,

A) from 29 to 99.95% by weight of a polyester,B) from 0.25 to 3.0% by weight of alkali metal oxoaluminates, or alkalimetal salts of cyanic acid, isocyanic acid, thiocyanic acid, ormetaboric acid, or a mixture of these,based on 100% by weight of A) and B), and also moreoverC) from 0 to 70% by weight of further additives, where the total of the% by weight values for A) to C) does not exceed 100%.

A DETAILED DESCRIPTION OF THE INVENTION

The molding compositions of the invention comprise, as component A),from 29 to 99.75% by weight, preferably from 98.0 to 99.7% by weight,and in particular from 99.0 to 99.65% by weight, of at least onethermoplastic polymer, based on components A) and B).

At least one of the polyesters in component A) is a semicrystallinepolyester. Preference is given to components A) which comprise at least50% by weight of semicrystalline polyesters. Said proportion isparticularly preferably 70% by weight (based in each case on 100% byweight of A)).

Based on 100% of the molding compositions made of A) to C) (i.e.inclusive of C)), these comprise

-   -   from 30 to 100% by weight of A)+B), preferably from 50 to 100%        by weight, and from 0 to 70% by weight of C), preferably from 0        to 50% by weight.

An essential constituent of the above relative magnitudes is that theproportion of component B) is always based on the polyester, since saidratio is intended to be within the abovementioned limits. The additivesC) can affect laser transparency. This effect is in essence dependent onthe scattering properties and absorption properties of the additives.The optical properties of the compounded material are in essence asummation of the optical properties of the matrix of the invention(components A+B) and of those of the additives (components C).

Polyesters A) used are generally based on aromatic dicarboxylic acidsand on an aliphatic or aromatic dihydroxy compound.

A first group of preferred polyesters is that of polyalkyleneterephthalates having in particular from 2 to 10 carbon atoms in thealcohol moiety.

Polyalkylene terephthalates of this type are known per se and aredescribed in the literature. Their main chain comprises an aromatic ringwhich derives from the aromatic dicarboxylic acid. There may also besubstitution in the aromatic ring, e.g. by halogen, such as chlorine orbromine, or by C₁-C₄-alkyl groups, such as methyl, ethyl, iso- orn-propyl, or n-, iso- or tert-butyl groups.

These polyalkylene terephthalates may be produced by reacting aromaticdicarboxylic acids, or their esters or other ester-forming derivatives,with aliphatic dihydroxy compounds in a manner known per se.

Preferred dicarboxylic acids are 2,6-naphthalenedicarboxylic acid,terephthalic acid and isophthalic acid or mixtures of these. Up to 30mol %, preferably not more than 10 mol %, of the aromatic dicarboxylicacids may be replaced by aliphatic or cycloaliphatic dicarboxylic acids,such as adipic acid, azelaic acid, sebacic acid, dodecanedioic acids andcyclohexanedicarboxylic acids.

Preferred aliphatic dihydroxy compounds are diols having from 2 to 6carbon atoms, in particular 1,2-ethanediol, 1,3-propanediol,1,4-butanediol, 1,6-hexanediol, 1,4-hexanediol, 1,4-cyclohexanediol,1,4-cyclohexanedimethanol and neopentyl glycol, and mixtures of these.

Particularly preferred polyesters (A) are polyalkylene terephthalatesderived from alkanediols having from 2 to 6 carbon atoms. Among these,particular preference is given to polyethylene terephthalate,polypropylene terephthalate and polybutylene terephthalate, and mixturesof these. Preference is also given to PET and/or PBT which comprise, asother monomer units, up to 1% by weight, preferably up to 0.75% byweight, of 1,6-hexanediol and/or 2-methyl-1,5-pentanediol.

The intrinsic viscosity of the polyesters (A) is generally in the rangefrom 50 to 220, preferably from 80 to 160 (measured in 0.5% strength byweight solution in a phenol/o-dichlorobenzene mixture in a ratio byweight of 1:1 at 25° C.) to ISO 1628.

Particular preference is given to polyesters whose carboxy end groupcontent is from 0 to 100 meq/kg of polyester, preferably from 10 to 50meq/kg of polyester and in particular from 15 to 40 meq/kg of polyester.Polyesters of this type may be produced, for example, by the process ofDE-A 44 01 055. The carboxy end group content is usually determined bytitration methods (e.g. potentiometry).

Particularly preferred molding compositions comprise, as component A), amixture of polyesters, at least one being PBT. An example of theproportion of the polyethylene terephthalate in the mixture ispreferably up to 50% by weight, in particular from 10 to 35% by weight,based on 100% by weight of A).

It is also advantageous to use PET recyclates (also termed scrap PET)optionally in a mixture with polyalkylene terephthalates, such as PBT.

Recyclates are generally:

-   1) those known as post-industrial recyclates: these are production    wastes during polycondensation or during processing, e.g. sprues    from injection molding, start-up material from injection molding or    extrusion, or edge trims from extruded sheets or films.-   2) post-consumer recyclates: these are plastics items which are    collected and treated after utilization by the end consumer.    Blow-molded PET bottles for mineral water, soft drinks and juices    are easily the predominant items in terms of quantity.

Both types of recyclate may be used either as regrind or in the form ofpellets. In the latter case, the crude recycled materials are isolatedand purified and then melted and pelletized using an extruder. Thisusually facilitates handling and free-flowing properties, and meteringfor further steps in processing.

The recycled materials used may either be pelletized or in the form ofregrind. The edge length should not be more than 10 mm and shouldpreferably be less than 8 mm.

Because polyesters undergo hydrolytic cleavage during processing (due totraces of moisture) it is advisable to predry the recycled material.Residual moisture content after drying is preferably <0.2%, inparticular <0.05%.

Another class to be mentioned is that of fully aromatic polyestersderiving from aromatic dicarboxylic acids and aromatic dihydroxycompounds.

Suitable aromatic dicarboxylic acids are the compounds previouslydescribed for the polyalkylene terephthalates. The mixtures preferablyused are made from 5 to 100 mol % of isophthalic acid and from 0 to 95mol % of terephthalic acid, in particular from about 50 to about 80% ofterephthalic acid and from 20 to about 50% of isophthalic acid.

The aromatic dihydroxy compounds preferably have the general formula

in which Z is an alkylene or cycloalkylene group having up to 8 carbonatoms, an arylene group having up to 12 carbon atoms, a carbonyl group,a sulfonyl group, an oxygen atom or sulfur atom, or a chemical bond, andin which m has the value from 0 to 2. The phenylene groups in thecompounds may also have substitution by C₁-C₆-alkyl groups or alkoxygroups, and fluorine, chlorine, or bromine.

Examples of parent compounds for these compounds are

dihydroxybiphenyl,di(hydroxyphenyl)alkane,di(hydroxyphenyl)cycloalkane,di(hydroxyphenyl)sulfide,di(hydroxyphenyl)ether,di(hydroxyphenyl)ketone,di(hydroxyphenyl)sulfoxide,α,α′-di(hydroxyphenyl)dialkylbenzene,di(hydroxyphenyl)sulfone, di(hydroxybenzoyl)benzene,resorcinol, and hydroquinone, and also the ring-alkylated andring-halogenated derivatives of these.

Among these, preference is given to

-   4,4′-dihydroxybiphenyl,-   2,4-di(4′-hydroxyphenyl)-2-methylbutane,-   α,α′-di(4-hydroxyphenyl)-p-diisopropylbenzene,-   2,2-di(3′-methyl-4′-hydroxyphenyl)propane, and-   2,2-di(3′-chloro-4′-hydroxyphenyl)propane,    and in particular to-   2,2-di(4′-hydroxyphenyl)propane,-   2,2-di(3′,5-dichlorodihydroxyphenyl)propane,-   1,1-di(4′-hydroxyphenyl)cyclohexane,-   3,4′-dihydroxybenzophenone,-   4,4′-dihydroxydiphenyl sulfone, and-   2,2-di(3′,5′-dimethyl-4′-hydroxyphenyl)propane    or a mixture of these.

It is, of course, also possible to use mixtures of polyalkyleneterephthalates and fully aromatic polyesters. These generally comprisefrom 20 to 98% by weight of the polyalkylene terephthalate and from 2 to80% by weight of the fully aromatic polyester.

It is, of course, also possible to use polyester block copolymers, suchas copolyetheresters. Products of this type are known per se and aredescribed in the literature, e.g. in U.S. Pat. No. 3,651,014.Corresponding products are also available commercially, e.g. Hytrel®(DuPont).

In the invention, the term polyester includes halogen-freepolycarbonates. Examples of suitable halogen-free polycarbonates arethose based on biphenols of the general formula

in which Q is a single bond, a C₁- to C₈-alkylene group, a C₂- toC₃-alkylidene group, a C₃- to C₆-cycloalkylidene group, a C₆- toC₁₂-arylene group, or else —O—, —S—, or —SO₂—, and m is a whole numberfrom 0 to 2.

The phenylene radicals of the biphenols can also have substituents,examples being C₁- to C₆-alkyl or C₁- to C₆-alkoxy.

Examples of preferred biphenols of this formula are hydroquinone,resorcinol, 4,4′-dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)propane,2,4-bis(4-hydroxyphenyl)-2-methylbutane and1,1-bis(4-hydroxyphenyl)cyclohexane. Particular preference is given to2,2-bis(4-hydroxyphenyl)propane and 1,1-bis(4-hydroxyphenyl)cyclohexane,and also to 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane.

Either homopolycarbonates or copolycarbonates are suitable as componentA, and preference is given to the copolycarbonates of bisphenol A, aswell as to bisphenol A homopolymer.

Suitable polycarbonates may be branched in a known manner, specificallyand preferably by incorporating from 0.05 to 2.0 mol %, based on thetotal of the biphenols used, of at least trifunctional compounds, forexample those having three or more phenolic OH groups.

Polycarbonates which have proven particularly suitable have relativeviscosities η_(rel) of from 1.10 to 1.50, in particular from 1.25 to1.40. This corresponds to an average molar mass M_(w) (weight average)of from 10 000 to 200 000 g/mol, preferably from 20 000 to 80 000 g/mol.

The biphenols of the general formula are known per se or can be producedby known processes.

The polycarbonates may, for example, be produced by reacting thebiphenols with phosgene in the interfacial process, or with phosgene inthe homogeneous-phase process (known as the pyridine process), and ineach case the desired molecular weight is achieved in a known manner byusing an appropriate amount of known chain terminators. (In relation topolydiorganosiloxane-containing polycarbonates see, for example, DE-A 3334 782.)

Examples of suitable chain terminators are phenol, p-tert-butylphenol,or else long-chain alkylphenols, such as 4-(1,3-tetramethylbutyl)phenol,as in DE-A 28 42 005, or monoalkylphenols, or dialkylphenols with atotal of from 8 to 20 carbon atoms in the alkyl substituents, as in DE-A35 06 472, such as p-nonylphenol, 3,5-di-tert-butylphenol,p-tert-octylphenol, p-dodecylphenol, 2-(3,5-dimethylheptyl)phenol and4-(3,5-dimethylheptyl)phenol.

For the purposes of the present invention, halogen-free polycarbonatesare polycarbonates made from halogen-free biphenols, from halogen-freechain terminators and optionally from halogen-free branching agents,where the content of subordinate amounts at the ppm level ofhydrolyzable chlorine, resulting, for example, from the production ofthe polycarbonates with phosgene in the interfacial process, is notregarded as meriting the term halogen-containing for the purposes of theinvention. Polycarbonates of this type with contents of hydrolyzablechlorine at the ppm level are halogen-free polycarbonates for thepurposes of the present invention.

Other suitable components A) which may be mentioned are amorphouspolyester carbonates, where phosgene has been replaced, during thepreparation, by aromatic dicarboxylic acid units, such as isophthalicacid and/or terephthalic acid units. For further details reference maybe made at this point to EP-A 711 810.

Other suitable copolycarbonates with cycloalkyl radicals as monomerunits have been described in EP-A 365 916.

It is also possible to replace bisphenol A with bisphenol TMC.Polycarbonates of this type are commercially available from Bayer withthe trademark APEC HT®.

The molding compositions of the invention comprise, as component B),from 0.25 to 3.0% by weight, preferably from 0.3 to 2% by weight, and inparticular from 0.35 to 1% by weight, based on 100% by weight of A)+B),of oxoaluminates of the alkali metals, or alkali metal salts of cyanicacid, isocyanic acid, thiocyanic acid, metaboric acid, or a mixture ofthese.

The carboxy end groups of the polyesters A) generally react with thesalt compounds B), whereupon the metal cation of the carbonate istransferred from the carbonate to the end group. The nucleating actionof component B) is detectable even at extremely low concentrations. Itis surprising that laser transparency falls with very low concentrationsof component B) and that a rise in laser transparency is not achieveduntil higher concentrations are reached.

It is preferable that the polyester A) comprises from 35 to 250 mmol/kgof polyester, preferably from 40 to 200 mmol/kg of polyester (based onA)+B)), where these concentration data are based on the respective anionof oxoaluminate, cyanate, isocyanate, thiocyanate, and metaborate.

Preferred alkali metals are sodium and/or potassium.

Preferred inorganic salts B) are sodium metaaluminate, sodium cyanate,sodium isocyanate, Na thiocyanate, Na metaborate, or a mixture of these.

Sodium aluminate is a water-soluble white powder which is generallyproduced by action of an excess of sodium hydroxide solution on Alsalts.

Processes for producing the other inorganic salts mentioned are known tothe person skilled in the art.

The molding compositions of the invention can comprise, as component C),from 0 to 70% by weight, in particular up to 50% by weight, of furtheradditives and processing aids, where these differ from B) and/or A),based on 100% by weight of A), B), and C).

Examples of conventional additives C) are amounts of up to 40% byweight, preferably up to 15% by weight, of elastomeric polymers (oftenalso termed impact modifiers, elastomers, or rubbers).

These very generally involve copolymers, which are preferably composedof at least two of the following monomers: ethylene, propylene,butadiene, isobutene, isoprene, chloroprene, vinyl acetate, styrene,acrylonitrile, and acrylates and, respectively, methacrylates havingfrom 1 to 18 carbon atoms in the alcohol component.

Polymers of this type are described, for example, in Houben-Weyl,Methoden der organischen Chemie, Vol. 14/1 (Georg Thieme Verlag,Stuttgart, Germany, 1961), pages 392-406, and in the monograph by C. B.Bucknall, “Toughened Plastics” (Applied Science Publishers, London,1977).

Some preferred types of such elastomers are described below.

Preferred types of such elastomers are those known as ethylene-propylene(EPM) and ethylene-propylene-diene (EPDM) rubbers.

EPM rubbers generally have practically no residual double bonds, whereasEPDM rubbers may have from 1 to 20 double bonds per 100 carbon atoms.

Examples which may be mentioned of diene monomers for EPDM rubbers areconjugated dienes, such as isoprene and butadiene, non-conjugated dieneshaving from 5 to 25 carbon atoms, such as 1,4-pentadiene, 1,4-hexadiene,1,5-hexadiene, 2,5-dimethyl-1,5-hexadiene and 1,4-octadiene, cyclicdienes, such as cyclopentadiene, cyclohexadienes, cyclooctadienes anddicyclopentadiene, and also alkenyl-norbornenes, such as5-ethylidene-2-norbornene, 5-butylidene-2-norbornene,2-methallyl-5-norbornene and 2-isopropenyl-5-norbornene, andtricyclodienes, such as 3-methyltricyclo[5.2.1.0^(2,6)]-3,8-decadiene,or a mixture of these. Preference is given to 1,5-hexadiene,5-ethylidenenorbornene and dicyclopentadiene. The diene content of theEPDM rubbers is preferably from 0.5 to 50% by weight, in particular from1 to 8% by weight, based on the total weight of the rubber.

EPM and EPDM rubbers may preferably also have been grafted with reactivecarboxylic acids or with derivatives of these. Examples of these areacrylic acid, methacrylic acid and derivatives thereof, e.g.glycidyl(meth)acrylate, and also maleic anhydride.

Copolymers of ethylene with acrylic acid and/or methacrylic acid and/orwith the esters of these acids are another group of preferred rubbers.The rubbers may also comprise dicarboxylic acids, such as maleic acidand fumaric acid, or derivatives of these acids, e.g. esters andanhydrides, and/or monomers comprising epoxy groups. These monomerscomprising dicarboxylic acid derivatives or comprising epoxy groups arepreferably incorporated into the rubber by adding to the monomer mixturemonomers comprising dicarboxylic acid groups and/or epoxy groups andhaving the general formula I, II, III or IV

where R¹ to R⁹ are hydrogen or alkyl groups having from 1 to 6 carbonatoms, and m is a whole number from 0 to 20, g is a whole number from 0to 10 and p is a whole number from 0 to 5.

R¹ to R⁹ are preferably hydrogen, where m is 0 or 1 and g is 1. Thecorresponding compounds are maleic acid, fumaric acid, maleic anhydride,allyl glycidyl ether and vinyl glycidyl ether.

Preferred compounds of the formulae I, II and IV are maleic acid, maleicanhydride and (meth)acrylates comprising epoxy groups, such as glycidylacrylate and glycidyl methacrylate, and the esters with tertiaryalcohols, such as tert-butyl acrylate. Although the latter have no freecarboxy groups, their behavior approximates to that of the free acidsand they are therefore termed monomers with latent carboxy groups.

The copolymers are advantageously composed of from 50 to 98% by weightof ethylene, from 0.1 to 20% by weight of monomers comprising epoxygroups and/or methacrylic acid and/or monomers comprising acid anhydridegroups, the remaining amount being (meth)acrylates.

Particular preference is given to copolymers composed of

from 50 to 98% by weight, in particular from 55 to 95% by weight, ofethylene,from 0.1 to 40% by weight, in particular from 0.3 to 20% by weight, ofglycidyl acrylate and/or glycidyl methacrylate, (meth)acrylic acid,and/or maleic anhydride, andfrom 1 to 45% by weight, in particular from 10 to 40% by weight, ofn-butyl acrylate and/or 2-ethylhexyl acrylate.

Other preferred (meth)acrylates are the methyl, ethyl, propyl, isobutyland tert-butyl esters.

Besides these, comonomers which may also be used are vinyl esters andvinyl ethers.

The ethylene copolymers described above may be produced by processesknown per se, preferably by random copolymerization at high pressure andelevated temperature. Appropriate processes are well known.

Other preferred elastomers are emulsion polymers whose production isdescribed, for example, by Blackley in the monograph “Emulsionpolymerization”. The emulsifiers and catalysts which can be used areknown per se.

In principle it is possible to use homogeneously structured elastomersor those with a shell structure. The shell-type structure is determinedby the sequence of addition of the individual monomers. The morphologyof the polymers is also affected by this sequence of addition.

Monomers which may be mentioned here, merely as examples, for theproduction of the rubber fraction of the elastomers are acrylates, suchas n-butyl acrylate and 2-ethylhexyl acrylate, correspondingmethacrylates, butadiene and isoprene, and also mixtures of these. Thesemonomers may be copolymerized with other monomers, such as styrene,acrylonitrile, vinyl ethers and with other acrylates or methacrylates,such as methyl methacrylate, methyl acrylate, ethyl acrylate or propylacrylate. The soft or rubber phase (with a glass transition temperatureof below 0° C.) of the elastomers may be the core, the outer envelope oran intermediate shell (in the case of elastomers whose structure hasmore than two shells). Elastomers having more than one shell may alsohave more than one shell made from a rubber phase.

If one or more hard components (with glass transition temperatures above20° C.) are involved, besides the rubber phase, in the structure of theelastomer, these are generally produced by polymerizing, as principalmonomers, styrene, acrylonitrile, methacrylonitrile, α-methylstyrene,p-methylstyrene, or acrylates or methacrylates, such as methyl acrylate,ethyl acrylate or methyl methacrylate. Besides these, it is alsopossible to use relatively small proportions of other comonomers here.

It has proven advantageous in some cases to use emulsion polymers whichhave reactive groups at their surfaces. Examples of groups of this typeare epoxy, carboxy, latent carboxy, amino and amide groups, and alsofunctional groups which may be introduced by concomitant use of monomersof the general formula

where the definitions of the substituents can be as follows:R¹⁰ is hydrogen or a C₁-C₄-alkyl group,R¹¹ is hydrogen or a C₁-C₈-alkyl group or an aryl group, especiallyphenyl,R¹² is hydrogen, a C₁-C₁₀-alkyl or C₆-C₁₂-aryl group or —OR¹³,R¹³ is a C₁-C₈-alkyl or C₆-C₁₂-aryl group, optionally havingsubstitution by O- or N-containing groups,X is a chemical bond or a C₁-C₁₀-alkylene or C₆-C₁₂-arylene group or

Y is O—Z or NH—Z, and

Z is a C₁-C₁₀-alkylene group or a C₆-C₁₂-arylene group.

The graft monomers described in EP-A 208 187 are also suitable forintroducing reactive groups at the surface.

Other examples which may be mentioned are acrylamide, methacrylamide andsubstituted acrylates or methacrylates, such as (N-tert-butylamino)ethylmethacrylate, (N,N-dimethylamino)ethyl acrylate,(N,N-dimethylamino)methyl acrylate and (N,N-diethylamino)ethyl acrylate.

The particles of the rubber phase may also have been crosslinked.Examples of crosslinking monomers are 1,3-butadiene, divinylbenzene,diallyl phthalate and dihydrodicyclopentadienyl acrylate, and also thecompounds described in EP-A 50 265.

It is also possible to use the monomers known as graft-linking monomers,i.e. monomers having two or more polymerizable double bonds which reactat different rates during the polymerization. Preference is given to theuse of compounds of this type in which at least one reactive grouppolymerizes at about the same rate as the other monomers, while theother reactive group (or reactive groups), for example, polymerize(s)significantly more slowly. The different polymerization rates give riseto a certain proportion of unsaturated double bonds in the rubber. Ifanother phase is then grafted onto a rubber of this type, at least someof the double bonds present in the rubber react with the graft monomersto form chemical bonds, i.e. the phase grafted on has at least somedegree of chemical bonding to the graft base.

Examples of graft-linking monomers of this type are monomers comprisingallyl groups, in particular allyl esters of ethylenically unsaturatedcarboxylic acids, for example allyl acrylate, allyl methacrylate,diallyl maleate, diallyl fumarate and diallyl itaconate, and thecorresponding monoallyl compounds of these dicarboxylic acids. Besidesthese there is a wide variety of other suitable graft-linking monomers.For further details reference may be made here, for example, to U.S.Pat. No. 4,148,846.

The proportion of these crosslinking monomers in the impact-modifyingpolymer is generally up to 5% by weight, preferably not more than 3% byweight, based on the impact-modifying polymer.

Some preferred emulsion polymers are listed below. Mention may first bemade here of graft polymers with a core and with at least one outershell, and having the following structure:

Type Monomers for the core Monomers for the envelope I 1,3-butadiene,isoprene, n-butyl styrene, acrylonitrile, methyl acrylate, ethylhexylacrylate, or a methacrylate mixture of these II as I, but withconcomitant use of as I crosslinking agents III as I or II n-butylacrylate, ethyl acrylate, methyl acrylate, 1,3-butadiene, isoprene,ethylhexyl acrylate IV as I or II as I or III, but with concomitant useof monomers having reactive groups, as described herein V styrene,acrylonitrile, methyl first envelope made of methacrylate, or a mixtureof these monomers as described under I and II for the core, secondenvelope as described under I or IV for the envelope

These graft polymers, in particular ABS polymers and/or ASA polymers,are preferably used in amounts of up to 40% by weight forimpact-modification of PBT optionally in a mixture with up to 40% byweight of polyethylene terephthalate. Appropriate blend products areobtainable with trademark Ultradur®S (previously Ultrablend®S from BASFAG).

Instead of graft polymers whose structure has more than one shell, it isalso possible to use homogeneous, i.e. single-shell, elastomers madefrom 1,3-butadiene, isoprene and n-butyl acrylate or from copolymers ofthese. These products, too, may be produced by concomitant use ofcrosslinking monomers or of monomers having reactive groups.

Examples of preferred emulsion polymers are n-butylacrylate-(meth)acrylic acid copolymers, n-butyl acrylate-glycidylacrylate or n-butyl acrylate-glycidyl methacrylate copolymers, graftpolymers with an inner core made from n-butyl acrylate or based onbutadiene and with an outer envelope made from the abovementionedcopolymers, and copolymers of ethylene with comonomers which supplyreactive groups.

The elastomers described can also be produced by other conventionalprocesses, e.g. via suspension polymerization.

Preference is likewise given to silicone rubbers as described in DE-A 3725 576, ER-A 235 690, DE-A 38 00 603, and EP-A 319 290.

It is, of course, also possible to use a mixture of the types of rubberlisted above.

Fibrous or particulate fillers C) that may be mentioned are glassfibers, glass beads, amorphous silica, asbestos, calcium silicate,calcium metasilicate, magnesium carbonate, kaolin, chalk, powderedquartz, mica, barium sulfate, and feldspar. The amounts used of fibrousfillers C) are up to 60% by weight, in particular up to 35% by weight,and the amounts used of particulate fillers are up to 30% by weight, inparticular up to 10% by weight.

Preferred fibrous fillers that may be mentioned are aramid fibers andpotassium titanate fibers, and particular preference is given here toglass fibers in the form of E glass. These can be used in the form ofrovings or of chopped glass in the forms commercially obtainable.

The amounts used of fillers that have high laser absorbency, for examplecarbon fibers, carbon black, graphite, graphene, or carbon nanotubes,are preferably below 1% by weight, particularly preferably below 0.05%by weight.

The fibrous fillers can have been surface-pretreated with a silanecompound in order to improve compatibility with the thermoplastic.

Suitable silane compounds are those of the general formula

(X—(CH₂)_(n))_(k)—Si—(O—C_(m)H_(2m+1))_(4-k)

where the definitions of the substituents are as follows:

X NH₂—,

HO—,

n is an integer from 2 to 10, preferably from 3 to 4m is an integer from 1 to 5, preferably from 1 to 2k is an integer from 1 to 3, preferably 1.

Preferred silane compounds are aminopropyltrimethoxysilane,aminobutyltrimethoxy-silane, aminopropyltriethoxysilane,aminobutyltriethoxysilane, and also the corresponding silanes whichcomprise a glycidyl group as substituent X.

The amounts generally used for surface coating of the silane compoundsare from 0.05 to 5% by weight, preferably from 0.1 to 1.5% by weight,and in particular 0.2 to 0.5% by weight (based on C).

Acicular mineral fillers are also suitable.

For the purposes of the invention, acicular mineral fillers are amineral filler with pronounced acicular character. An example that maybe mentioned is acicular wollastonite. The L/D (length to diameter)ratio of the mineral is preferably from 8:1 to 35:1, with preferencefrom 8:1 to 11:1. The mineral filler can optionally have been pretreatedwith the abovementioned silane compounds; however, the pretreatment isnot essential.

The thermoplastic molding compositions of the invention can comprise, ascomponent C), conventional processing aids, such as stabilizers,oxidation retarders, agents to counteract decomposition by heat anddecomposition by ultraviolet light, lubricants and mold-release agents,colorants, such as dyes and pigments, plasticizers, etc.

Examples that may be mentioned of oxidation retarders and heatstabilizers are sterically hindered phenols and/or phosphites,hydroquinones, aromatic secondary amines, such as diphenylamines,various substituted members of said groups, and mixtures of these inconcentrations which are up to 1% by weight, based on the weight of thethermoplastic molding compositions.

UV stabilizers that may be mentioned, the amounts of which used aregenerally up to 2% by weight, based on the molding composition, arevarious substituted resorcinols, salicylates, benzotriazoles, andbenzophenones.

Colorants that can be added comprise inorganic and organic pigments, andalso dyes, such as nigrosin, and anthraquinones. Particularly suitablecolorants are mentioned by way of example in EP 1722984 B1, EP 1353986B1, or DE 10054859 A1.

Preference is further given to esters or amides of saturated orunsaturated aliphatic carboxylic acids having from 10 to 40, preferablyfrom 16 to 22, carbon atoms with saturated aliphatic alcohols or amineswhich comprise from 2 to 40, preferably from 2 to 6, carbon atoms.

The carboxylic acids can be monobasic or dibasic. Examples that may bementioned are pelargonic acid, palmitic acid, lauric acid, margaricacid, dodecanedioic acid, behenic acid, and with particular preferencestearic acid, and capric acid, and also montanic acid (a mixture offatty acids having from 30 to 40 carbon atoms).

The aliphatic alcohols can be mono- to tetrahydric. Examples of alcoholsare n-butanol, n-octanol, stearyl alcohol, ethylene glycol, propyleneglycol, neopentyl glycol, and pentaerythritol, preference being givenhere to glycerol and pentaerythritol.

The aliphatic amines can be mono- to trifunctional. Examples of theseare stearylamine, ethylenediamine, propylenediamine,hexamethylenediamine, and di(6-aminohexyl)amine, particular preferencebeing given here to ethylenediamine and hexamethylenediamine. Preferredesters or amides are correspondingly glycerol distearate, glyceroltristearate, ethylenediamine distearate, glycerol monopalmitate,glycerol trilaurate, glycerol monobehenate, and pentaerythritoltetrastearate.

It is also possible to use a mixture of various esters or amides, oresters combined with amides, in any desired mixing ratio.

The amounts usually used of further lubricants and mold-release agentsare usually up to 1% by weight. It is preferable to use long-chain fattyacids (e.g. stearic acid or behenic acid), salts of these (e.g. Castearate or Zn stearate), or montan waxes (mixtures made ofstraight-chain, saturated carboxylic acids having chain lengths of from28 to 32 carbon atoms), or else Ca montanate or Na montanate, or elselow-molecular-weight polyethylene waxes or low-molecular-weightpolypropylene waxes.

Examples that may be mentioned of plasticizers are dioctyl phthalate,dibenzyl phthalate, butyl benzyl phthalate, hydrocarbon oils, andN-(n-butyl)benzenesulfon-amide.

The molding compositions of the invention can also comprise from 0 to 2%by weight of fluorine-containing ethylene polymers. These are polymersof ethylene having fluorine content of from 55 to 76% by weight,preferably from 70 to 76% by weight.

Examples here are polytetrafluoroethylene (PTFE),tetrafluoroethylene-hexafluoropropylene copolymers, ortetrafluoroethylene copolymers having relatively small proportions(generally up to 50% by weight) of copolymerizable ethylenicallyunsaturated monomers. These are described by way of example bySchildknecht in “Vinyl and Related Polymers”, Wiley-Verlag, 1952, pages484 to 494, and by Wall in “Fluoropolymers” (Wiley Interscience, 1972).

The form in which these fluorine-containing ethylene polymers arepresent in the molding compositions is that of a homogeneous dispersion,and their d₅₀ (number-average) particle size is preferably in the rangefrom 0.05 to 10 μm, in particular from 0.1 to 5 μm. These small particlesizes can particularly preferably be achieved via use of aqueousdispersions of fluorine-containing ethylene polymers and incorporationof these into a polyester melt.

The thermoplastic molding compositions of the invention can be producedby processes known per se, by mixing the starting components inconventional mixing apparatuses, such as screw extruders, Brabendermixers, or Banbury mixers, and then extruding the same. The extrudatecan be cooled and comminuted after the extrusion. It is also possible topremix individual components (e.g. applying component B) to the pellets,for example in a drum), then adding the remaining starting materialsindividually and/or after they have been likewise mixed. The mixingtemperatures are generally from 230 to 290° C. Component B) can alsopreferably be added to the extruder inlet by the hot-feed or directmethod.

In another preferred method of operation, components B), and alsooptionally C), can be mixed with a polyester prepolymer, and compoundedand pelletized. The resultant pellets are then solid-phase condensedunder inert gas continuously or batchwise at a temperature below themelting point of component A) until the desired viscosity has beenreached.

The molding compositions that can be used by the invention are suitablefor producing laser-transparent moldings. The laser transparency ofthese is preferably at least 33%, in particular at least 40% (measuredat 1064 nm on moldings of thickness 2 mm, by the test method describedin the examples).

The invention uses laser-transparent moldings of this type to producemoldings by means of laser transmission welding processes.

The laser-absorbent molding used can generally comprise moldings made ofany of the materials that are laser-absorbent. By way of example, thesecan be composite substances, thermosets, or preferred moldings made ofspecific thermoplastic molding compositions. Suitable thermoplasticmolding compositions are molding compositions which have adequate laserabsorption in the wavelength range used. By way of example, suitablethermoplastic molding compositions can preferably be thermoplasticswhich are laser-absorbent through addition of inorganic pigments, suchas carbon black, and/or through addition of organic pigments or of otheradditives. Examples of suitable organic pigments for achieving laserabsorption are preferably IR-absorbent organic compounds such as thosedescribed by way of example in DE 199 16 104 A1.

The invention further provides moldings and/or molding combinations towhich moldings of the invention were bonded by laser transmissionwelding.

Moldings of the invention have excellent suitability for application ina long-lasting and stable manner to laser-absorbent moldings by thelaser transmission welding process. They therefore have particularsuitability for materials for covers, housings, add-on components, andsensors, for example for applications in the motor-vehicle, electronics,telecommunications, information-technology, computer, household, sports,medical, or entertainment sector.

EXAMPLES Component A/1

Polybutylene terephthalate with an intrinsic viscosity of 130 ml/g andwith carboxy end group content of 34 meq/kg (Ultradur® B 4500 from BASFSE) (IV measured in 0.5% strength by weight solution ofphenol/o-dichlorobenzene, 1:1 mixture at 25° C., to ISO 1628).

Component B

Molecular formula Name (molar mass, g/mol) B1 Sodium cyanate NaOCN (65)B2 Sodium thiocyanate NaSCN (81) B3 for comparison Sodium hypophosphiteNaH₂PO₂ (88) B4 for comparison Tetrasodium diphosphate Na₄P₂O₇ (266) B5Sodium metaborate NaBO₂ (66) B6 Sodium metaaluminate NaAlO₂ (82) B7 forcomparison Sodium tungstate Na₂WO₄ (294) B8 for comparison Sodiumsulfite Na₂SO₃ (142)

The molding compositions were produced in a ZSK 25 with a flattemperature profile at from 250 to 260° C. and with pelletization.

Laser Transparency Measurement

A thermoelectric power measurement was used to determine lasertransmittance at wavelength 1064 nm. The measurement geometry was set upas follows: a beam divider (SQ2 nonpolarizing beam divider fromLaseroptik GmbH) was used to divide a reference beam of power 1 watt atan angle of 90° from a laser beam (diode-pumped Nd-YAG laser ofwavelength 1064 nm, FOBA DP50) with total power of 2 watts. Thereference beam impacted the reference sensor. That portion of theoriginal beam that passed through the beam divider provided themeasurement beam likewise with power of 1 watt. This beam was focused tofocal diameter 0.18 μm via a mode diaphragm (5.0) behind the beamdivider. The laser transparency (LT) measurement sensor was positioned80 mm below the focus. The test sheet was positioned 2 mm above the LTmeasurement sensor. The dimensions of the injection-molded test sheetsused were 60*60*2 mm³ and they had edge gating. The measurement was madein the middle of the sheet (point of intersection of the two diagonals).The settings used for the injection-molding parameters were as follows:

Melt temp. Mold temp. Injection rate Hold pressure [° C.] [° C.] [cm³/s][bar] Unreinforced 260 60 48 600 materials Reinforced 260 80 48 600materials

The total measurement time was 30 s, and the result of the measurementis determined within the final 5 s. The signals from the referencesensor and measurement sensor were recorded simultaneously. Themeasurement process begins with insertion of the specimen.

Transmittance, and therefore laser transparency, was obtained from thefollowing formula:

LT=(signal(measurement sensor)/signal(reference sensor))×100%.

This measurement method excluded variations in the laser system andsubjective read-out errors.

The average LT value for a sheet was calculated from at least fivemeasurements. For each material, the average value was calculated on 10sheets. The average values from the measurements on the individualsheets were used to calculate the average value, and also the standarddeviation, for the material.

The tensile test was carried out to ISO 527, and impact resistance wasmeasured to ISO 179.

Calorimetric studies were carried out by means of DSC to ISO 11357,heating and cooling rate 20 K/min. The crystallization peak temperatureT_(PC) was determined in the first cooling procedure.

TABLE 1 Amount of Amount of nucl. LT T_(pc) nucl. [mmol/kg @ 1064 nm(pellets) Component [% by wt.] PBT] [% T] [° C.] Reference*⁾ 0 0 30 185B1 0.5 77 47 198 B2 0.5 62 39 199 B3*⁾ 0.5 57 23 191 B4*⁾ 0.5 75 32 184B4*⁾ 1 150 32 185 B5 0.5 75 43 196 B6 0.5 61 48 196 B7*⁾ 1 68 26 185B8*⁾ 0.5 70 24 194 *⁾for comparison

TABLE 2 Amount Amount of nucl. of nucl. LT @ Modulus of Tensile Tensilestrain IV T_(pc) [% by [mmol/kg 1064 nm elasticity strength at break(pellets) (pellets) Component wt.] PBT] [% T] [MPa] [MPa] [%] [mL/g] [°C.] Reference*) 0 0 30 2500 56 170 130 185 B1* 0.1 15 26 2500 56 15 122185 B1* 0.2 31 23 2500 56 15 122 188 B1 0.3 46 41 2650 59 16 123 196 B10.4 62 44 2650 59 16 123 197 B1 0.5 77 47 2650 59 16 122 198 B1 0.75 11549 2650 59 16 122 198 B1 1 154 50 2700 59 16 122 198 B6* 0.1 12 22 250056 18 121 186 B6* 0.2 24 25 2550 58 17 120 190 B6 0.3 37 34 2600 59 17120 194 B6 0.4 49 43 2650 60 16 120 194 B6 0.5 61 48 2650 60 16 120 196B6 0.75 92 53 2700 60 16 117 198 B6 1 122 57 2700 60 16 115 199 *)forcomparison

1-8. (canceled)
 9. A process for producing a laser-transparent moldingwhich comprises utilizing a thermoplastic molding compositioncomprising, as essential components, A) from 29 to 99.95% by weight of apolyester, B) from 0.25 to 3.0% by weight of alkali metal oxoaluminates,or alkali metal salts of cyanic acid, isocyanic acid, thiocyanic acid,or metaboric acid, or a mixture of these, based on 100% by weight of A)and B), and also moreover C) from 0 to 70% by weight of furtheradditives, where the total of the % by weight values for A) to C) doesnot exceed 100%.
 10. The process according to claim 9, comprising anamount of component B) which is (based on A) and B)) from 35 to 250mmol/kg of polyester, where these concentration data are based on therespective anion of the acid.
 11. The process according to claim 9,wherein the laser transparency of the molding is at least 33% (measuredat 1064 nm on a molding of thickness 2 mm).
 12. The process according toclaim 9, wherein the alkali metal of component B) is sodium.
 13. Theprocess according to claim 9, where component B) is composed of sodiumcyanate, sodium thiocyanate, sodium metaborate, sodium aluminate, or amixture of these.
 14. The process of according to claim 9 for producingmoldings by means of laser transmission welding processes.
 15. A processfor producing welded moldings, which comprises using laser transmissionwelding to bond laser-transparent moldings produced according to claim14 to laser-absorbent moldings.
 16. A process for producing weldedmoldings, which comprises using laser transmission welding to bondlaser-transparent molding produced according to claim 9 tolaser-absorbent moldings.
 17. A welded molding obtainable according toclaim 14, which is suitable for applications in the electrical,electronics, telecommunications, information-technology, computer,household, sports, medical, motor-vehicle, or entertainment sector.